Here's a situation where we all encounter every day in our commute:
From stop light: speed up to ~40-45mph then coast to next red light, and maximize on regen to stop.

My question is: which is better for overall FE during the acceleration:

1. Slow and constant acceleration (not EV only "slow"), keeping the ICE reving 2000-2500 rpm only, for about ~25-30 seconds until 40mph is reached.

2. Apply harder acceleration for 2-4sec up to 3k rev on the ICE, then "FS - Fake Shift" by easing off on accelerator (so RPM backs down to <2k), then repeat for 2 more time until 40mph is reached. Basically, pulse acc. 3 times with 3 FS to get up to speed. The first acc. gets you to ~20mph, then 2nd to 35mph, then the third to 40+mph. The FS parts must allow for RPM to get below 2k.

The reason I ask is this: I notice that battery assist is used much more (on the battery power dail) on harder acc., and pratically none when using constant acc. (doesnt have to be slow, just constant acc). On top of that, when FS occurs, the battery is "recharged" from the high reved ICE energy (hence you have to FS back down to <2k rpm to maximize the charge recapture).

So if you slow acc. you use ICE energy only (or mostly) for long period of acc., and recapture only some of that back on the next red light by regen.

But if you pulse acc., you use a lot of battery power, which you get back in both the FS, and the regen when stopping. Sure your ICE revs higher, but in much shorter time period. And emotor is more efficient at low revs...oh and people behind you dont get mad and try to pass you up and cursing at hybrid drivers.

Maybe someone with scanguage info can answer the question?

 

The process, ANY process, of charging the hybrid battery is very lossy. Intentionally creating a need to recharge the hybrid battery, accelerate and then coast, "pulse and glide", is therefore counter-productive.

The modeling of the hybrid system during the design phase would have only involved inadvertent, unavoidable, use of regenerative braking, slowing and or stopping because traffic conditions forced you to do so. Not conditions, by any means, created artificially by modifying the way you drive a hybrid vs an ordinary vehicle while being conscientous of FE.

For instance if I could disable my Prius' techique of using the hybrid electrics during highway cruising I would be perfectly happy with the resulting slower acceleration rate of just the ICE in return for the substantially improved FE on the freeway.

Absent any modification of the Prius hybrid control system, if there is even a slight loss of cruise controlled roadspeed on the freeway the electrics will kick in and provide "boost" to more quickly return to the "set" speed. In 150 miles of relatively constant speed level freeway driving the hybrid battery recharge ICE cycle will be needed 6 or 7 times.

So the losses involved in charging the hybrid battery using the ICE and those involved in the use of the energy stored in the hybrid battery are a net loss. Neevr to be recovered. That's why hybrid hwy FE is so horrible vs an equivalently equipped/weight ICE only vehicle.

The electric drive motors are used each time even a slight level of (re)acceleration is required and then eventually the hybrid batteries will be discharged to the point that the system will default into using the very lossy ICE method to bring them back up close to the "top-off" level. Only "close" because the system always leaves some "room" in the event "free" energy become available via regenerative braking.

So, bottom line is that it is highly likely the best FE can be obtained by driving a hybrid in the same way you would an ordinary car provided you were being sensitive, conscientous, of the need to conserve fuel.

Being conscientous of FE, you would not be a leadfoot in the ordinary vehicle so why not exhibit the same technique in a hybrid?

Therein lies the best FE.

 

Willard, that may or maynot work for the Prius, but it is not true in the FEH/MMH. If you can push a Prius close to like Wayne Gerdes (120mpg), I'm all ears and have respect for your abilities. It's clear to me you don't understand what is best for FE in the FEH/MMH, but I'm trying to express this in a productive way, and not be nasty.

For those who know how to double EPA estimates on driving segments, they know the best ways to handle acceleration and FE.

My today's average was 47.9mpg according to my scangauge. It is still warm here, and I could hear the A/C compressor kicking in when the ICE restarted to charge. Here are my SG readings for today:

47.9 average

24mph average

53mpgh max

2.7 hrs driving

4803rpm max (had to make the light)

67.3 miles traveled

1.4 gal burned

This is from a cold start this morning with a low SoC and a low SoC parked tonight. When it gets cooler, my numbers will be much higher.

For details on how I accelerate and P&G, see my article at:
http://www.cleanmpg.com/forums/showthread.php?t=350

If anyone can help us get better FE, please let us know.

GaryG

 

Gary, I consider the Prius nothing more or less than a tool. A vehicle used to get me from point A to point B. Sure, I could likely experiment, as does wayne, and get improved FE, or maybe even Stellar FE, but to what end?

Drive, she said, and drive, he did.

Personally if I really wanted to improve FE I would be adding an inverter style genset of the approximate capacity (5KW??) required to move the vehicle along briskly on a flat roadbed. The genset would idle along or maybe not even be running unless the hybrid battery dropped below, say, 1/3 charge, and then the genset would run WOT, the most efficient region for any otto engine, until the batteries were again topped off.

There would then be no reason EVER to use the OEM ICE for hybrid battery charging, for which it is EXTREMELY inefficient. Only regenerative braking and/or the more efficient (vs the ICE) genset would provide enough energy to keep the hybrid battery in an acceptable state of charge.

Additionally the genset could be run from my natural gas supply at home with a commercially available CNG fueling "station" currently available in the marketplace.

 

But I get 29 on the freeway in my 4WD FEH (exactly the EPA estimate amazingly)......The 4WD 6cylinder gets 17 on the freeway... For some reason I can't get to the ford site right now but I think the 4 cylinder 2.3 non hybrid is rated 24MPG.....

Why is my hybrid hwy so horrible vs an equivalent weight ICE only vehicle... It still seems to have an advantage... just not as large of one.

 

Or even more fun, use the posters at Edmunds as your Escape sampling base. For the 4WD Escape, the average is 14 MPGs mixed. Contrasted against my 4WD FEH at 33.4, and that's more then 238% the FE of the nonhybrid equivalent. (Yeah, I know, a large sample base at Edmunds vs my own personal FE isn't exactly fair.)

 

I find highway mileage to actually be excellent in my Mariner Hybrid (4wd). I regularly get 33-35mpg just by cruising at the speed limit. In the city, due to all my short trips and red lights I am only getting about 28mpg.

As for acceleration, I wondered something similar....whether it was better to quickly accelerate to cruising speed and then level out or to gradually increase speed until you reach cruising. It seems to me that the longer you spend cruising at a more efficient speed the better.

Now, I just made up these numbers but maybe someone with a scanguage can actually test the fuel usage.

Accelerating from a stop to 60mph and crusing - distance of 5 miles.

Example 1: Hard acceleration
est. FE of 10mpg for 1 mile of acceleration = .10 gal burned
est. FE of 35mpg for 4 miles of cruising = .12 gal burned
total fuel used = .22 gallons

Example 2: Gradual acceleration
avg. FE of 15 mpg for 2.5 miles of acceleration = .17 gal burned
est. FE of 35 mpg for 2.5 miles of cruising = .07 gal burned
total fuel used = .24 gallons

Now, OBVIOUSLY these numbers are totally made up, but I wonder whether one method is better than the other. Personally, I wouldn't bother doing something like multiple FS's during acceleration, but if there is an advantage to gradual or rapid acceleration I would choose the better one.

 

Thanks guys, but TimK got the gist of what I was trying to ask.

I just added the extra thing about multiple acceleration because I notice the rather large energy flow from the engine to the battery when you fake shfit, therefore it seems you get a lot of that acceleration energy back to your battery.

The multiple fake shift is like dring a stick shift, which seems more efficient.

TimK's numbers are made up, but if its close that's 10%. Do that many times during the course of the drive per day, and it adds up.

 

Obviously, if the hybrid battery charge is at or near the top, pulse and glide offers no advantage.

 

True, but it might be beneficial to pulse and pulse but not worry about recharge. I say that because I see that sudden/quick power bursts at speed seem to come from the electric motors. I was also wondering whether repeated bursts of acceleration might be more efficient than either a steady accel or hard accel. It might not make for a pleasant ride while you do it though....unless you take dramamine first.